The present invention relates to an electronic converter, in particular to a current system and a control method applied to the electronic converter in the DC-to-AC, AC-to-AC, AC-to-DC or DC-to-DC conversion process.
There are many kinds of modern electronic converters and control techniques. Classified by different forms, the control techniques of the electronic converter include the following types:
(1) According to the AC outputting frequency of the inverting portion of the converter, the inversion is classified into power frequency inversion, intermediate-frequency inversion and high-frequency inversion. Power frequency usually refers to 50-60 Hz; the frequencies of the intermediate-frequency inversion usually are 400 Hz to dozens of KHz, and those of the high-frequency inversion are usually dozens of KHz to MHz.
(2) According to the phase number input by the inversion portion of the converter, the inversion is classified into single-phase inversion, three-phase inversion and multi-phase inversion.
(3) According to the energy output target of the inversion portion of the converter, the inversion is classified into active inversion and passive inversion.
(4) According to the form of the main circuit of the inversion part of the converter, the inversion is classified into single-end type, push-pull type, half-bridge type and full-bridge type inversion.
(5) According to the types of the main switching devices of the inversion part of the converter, the inversion is classified into thyristor inversion, transistor inversion, field-effect-tube inversion and IGBT inversion.
(6) According to the stable parameters output by the inversion portion of the converter, the inversion is classified into voltage type inversion and current type inversion.
(7) According to the waveform of the voltage or current output by the inversion portion of the converter, the inversion is classified into sine wave output inversion and non-sine wave output inversion.
(8) According to the control mode of the inversion portion of the converter, the inversion is classified into the pulse frequency modulated (PFM) inversion and pulse width modulated (PWM) inversion.
(9) According to the working mode of the switching circuit of the inversion portion of the converter, the inversion is classified into resonance inversion, fixed-frequency hard switching type inversion and fixed-frequency soft switching type inversion.
The digital control of the electronic converter is the current technical development trend and is also the modern inversion technology development trend. The digital control greatly simplifies the hardware circuit and improves the stability, reliability and control precision of the system, but still has the following problems:
(a) In the traditional analog control mode, the power of the electronic converter is small;
(b) The control signal sources in the circuit system are affected by the parameter changes of the analog devices, for example changes of the temperature, humidity, altitude, electromagnetic field, energy source and load, so the performance of the whole converter also changes, thus resulting in unstable performance of the whole system.
(c) In the analog control mode, the electronic converter is controlled in a closed-loop feedback mode, the parameters may derivate in the whole circuit, and when the deviating parameters are superposed and amplified, system shutdown is generated very easily; in particular, the current or voltage index of the key switching devices rises, leading to the avalanche effect.
(d) As the power of the electronic converter increases, the effects on the electromagnetic compatibility of the power grid also increase; only some power factor adjusting circuits can be negatively used and some passive filter circuits are added to reduce the conversion efficiency of the system.
(e) AT present, the electronic converter has a weak capability of controlling the load, in particular in the high-frequency conversion process, easily generates extra excessive electromagnetic energy, causing magnetic pollution to the surroundings; when the load changes, the slow reaction in the converter easily causes system failure.